The present invention relates to an ultraviolet light permeable filter for a flaw detection light and a method for a detection of flaws.
In a prior art, according to JIS(Japan Industrial Standard), in order to perform a fluorescent penetrant liquid detection method test and a fluorescent magnetic powder detection (=magnaflux) method test, an ultraviolet detection light (this is also called a black light among those skilled in the art) is adopted, wherein the light is emitted from a metal halide lamp and an ultraviolet light filter so that the fluorescent penetrant liquid and magnetic powder are excited to emit radiation.
For example, in the method as already disclosed, the ultraviolet flaw detection light comprising the metal halide lamp and the ultraviolet light permeable filter equipped with a minimum wave length of 385xc2x15 nm which can be recognized with normal eyesight is provided. An inspector can lessen his fatigue or avoid his mistakes caused by fatigue during blue-violet radiation using a wave length below 400 nm.
In the field test of the fluorescent penetrant liquid method or the fluorescent magnetic powder method for checking a flaw on an irregular surface in a minor area where a marketed ultraviolet flaw detection light comprising the ultraviolet light permeable filter and the metal halide lamp is used, a serious problem exists. The inspector has difficulty in checking the flaw because he is forced to recognize with his eyes a reddish halation mixed by a red and pale blue radiations which are caused by reflected light from a test display according to the angle between radiated light and the inspector""s eyes toward the display. When the flaw exists on the spot of the halation, especially a reddish halation, the inspector might miss checking the relative flaw. As a result, an accurate flaw detection cannot be attained by the inspection on an irregular surface in a minor area for finished work.
The present inventor has done research and experiments to provide an ultraviolet light permeable filter which prevents the occurrence of halation, especially reddish halation which is the main cause of overlooking a flaw during the inspection. As a result, this inventor has confirmed that visible radiation wave length in the ranges of 380 nmxcx9c410 nm and 694 nmxcx9c780 nm penetrates through a prior marketed ultraviolet light permeable filter. This prior art uses various kinds of ultraviolet flaw detection lights composed of metal halide lamps. The radiation in the above ranges reflects on the test display to produce a reddish halation. At the same time, the inventor has found that the reddish halation is avoided when the radiation in the range of 694 nmxcx9c780 nm does not penetrate the filter.
In order to realize the above purpose, the following procedures are adopted.
This invention provides a device of a dielectric multi-film layer which is formed on the surface of the ultraviolet light permeable filter glass, whereas visible radiation in the range of 694 nmxcx9c780 nm reflects on the filter and does not penetrate therethrough.
The invention also provides a device of the filter where the dielectric multi-film layer is composed of plural layers of low refractivity material and of high refractivity material stacked in alternating layers of low refractivity and high refractivity material.
This invention further provides a device of any filter as mentioned so far where the multi-film layer is while a layer of high refractivity material is sandwiched between layers of low refractivity material and the obtained composite is a plurality of layers thick.
Further, the flaw detection light of the present invention is equipped with any of said filters.